Chemical process units such as alkylation units require introduction of two liquid reactants and mixture of those reactants. Mixture is facilitated generally by an impeller blade. In known assemblies, the impeller blade is driven by a two-piece drive shaft. The impeller is situated in a removable end portion of the reactor on one end of the alkylation unit. Persons skilled in the art sometimes call this portion of the reactor a "hydraulic head." The two-piece drive shaft is disposed through an aperture in the hydraulic head and connected on one end to the impeller blade and on the other end to, e.g., an electric motor.
The liquid reactants, e.g., in an alkylation unit, pose environmental and safety hazards and therefore it is desirable to avoid leakage of the liquids out of the reactor. The drive shaft disposed through an aperture in the hydraulic head therefore must utilize a seal (a "mechanical seal") at the location where the drive shaft meets the aperture. The mechanical seal is necessary to keep the products and reactants from leaking out of the reactor. The mechanical seal typically includes integral bearing for supporting the drive shaft.
A second weight-supporting bearing is used to support the two-piece drive shaft. The second weight-supporting bearing is located along the two-piece drive shaft at a point between the aperture in the hydraulic head and the motor shaft.
This mechanical seal has a limited life and must be replaced and/or maintained from time-to-time. Such maintenance and/or replacement requires shutting down the process unit.
In theory, the advantage of the existing two-piece drive shaft (also referred to as a "split drive shaft") is that it allows on-site maintenance and/or replacement of the mechanical seal. This is done by detaching the motor shaft coupling and the split shaft coupling. The split shaft coupling is typically accessed by an access door in the bearing housing. The bearing housing is detached from the hydraulic head. The oil seal and bearing housing remain attached to one portion of the split drive shaft. The oil seal and bearing housing cannot be removed in the field from its associated piece of the split drive shaft. These detachments result in access to the mechanical seal for maintenance/replacement. In the absence of a split drive shaft, the procedure would have to be as follows. The motor shaft is disconnected, the hydraulic head is disconnected, and the whole assembly is brought into a repair facility for removal of the oil seal. Only then is the mechanical seal accessible for maintenance/replacement.
The disadvantage of the two-piece drive shaft, however, is that upon reinstallation of the bearing housing, the connection point of the two portions of the two-piece drive shaft must be precisely aligned within narrow tolerances. Any misalignment results in wobble, vibration, and the resulting stress forces to the assembly. Such forces result in premature and possibly catastrophic outage of the contactor assembly. The precise alignment necessary to avoid these premature outages is manpower intensive and requires 6-8 hours to complete. In practice, the theoretical advantage of maintaining the mechanical seal is not possible. This is due to the great difficulty of sufficiently aligning the two-piece drive shaft in the field. In practice, adequate alignment is only possible in the shop. This necessitates removal of the hydraulic head, thus negating the intended advantages of the two-piece drive shaft.
It would be desirable to have a contactor assembly which did not have the deficiencies of requiring precise alignment on installation. Accordingly, the contactor assembly of the invention provides a solution to this problem. It has now been discovered that a contactor assembly having a one-piece drive shaft avoids the deficiencies of the existing two-piece drive shaft.